The tendency of plastics, glasses, and other relatively soft materials to be scratched or otherwise marred during normal handling and use has limited the applications of such materials and has limited the useful life of articles prepared from such materials. Scratches on transparent plastic windows or screens can severely limit the useful life of the product and can lead to significant consumer dissatisfaction.
Several techniques have been used to provide scratch resistance to plastic and other relatively soft materials. Such techniques have generally involved the application of a continuous, hard, protective coating to the soft substrate. In one method, a resin coating is applied to the substrate and then cured or hardened in place. Although this technique can be applied to many plastic surfaces, the cured resin coating itself may not have a significantly higher degree of scratch resistance than the underlying plastic substrate. Even when the cured resin does impart a degree of scratch resistance, the cured resin may not adhere strongly to the substrate. In such cases, especially where the product is subject to flexing action or temperature variations, the bond between the cured protective resin and the substrate is prone to failure.
Vacuum deposition techniques have also been used to form protective coatings in the form of dense hard films on substrate surfaces. The hard films produced generally lack flexibility and are, therefore, subject to cracking or "crazing" due to either temperature changes or flexing motions in the product. Furthermore, vacuum deposition techniques do not easily lend themselves to coating many plastic substrates due to the elevated temperatures normally required and the long exposure to the temperatures necessary to form the protective coating. The technique, which is relatively expensive and time consuming, is generally limited to more expensive and higher value added products.
Diamond (the hardest naturally occurring material known) and other similarly hard materials have not been used as films or coatings on relatively soft materials such as plastic to provide scratch resistance or improved wear characteristics. Even if such films could be prepared, they would be extremely expensive and would be subject to similar "crazing" effects as the hard resin coatings of the prior art.
It is desirable, therefore, to provide new protective surfaces or coatings for plastic, glass, metal, and composite materials which provide a high degree of scratch resistance and improved wear characteristics. It is also desirable to provide plastic articles with a degree of scratch resistance heretofore unobtainable. It is also desirable to provide new protective surfaces or coatings which are not prone to "crazing" effects normally associated with continuous protective films. It is also desirable to provide new protective surfaces or coatings which can be easily formed at a relatively low cost on a wide variety of substrate materials and on a wide variety of shaped products. It is also desirable to provide transparent scratch resistance surfaces or coatings. The present invention provides such methods and products.